Winding transformer

[camerart]

Hi,

I need a power supply for a battery charger. Ideally it needs to be 24V 40A at minimum, but it will work with lower inputs.

I have an old 800W microwave, is there a way that I could modify the transformer to power it. I can see that it would be underpowered, but could it work, and what would I need to do?

Camerart.

 

[Taylortwocities]

...

 

[ban-all-sheds]

I have an old 800W microwave, is there a way that I could modify the transformer to power it.

Will that be the transformer with an output voltage measured in the thousands of volts which powers the magnetron? Now that we no longer have CRT TVs, the transformer in your microwave oven is the most lethal electrical component you can lay hands on in your home.

How do you think you might modify it to output a lower voltage?

How do you think that a secondary winding designed to carry less than 1A could be modified to be able to carry 100 times as much? Or modify the primary winding to carry 10x as much if you reverse the transformer?

what would I need to do?

You would need to go and buy a suitable charger.

From the suggestion you are making and the questions you are asking (particularly the last one) it's clear that you really know nowhere near enough about electronics and basic electrical theory to be doing this work. Please don't try - you could easily injure or even kill yourself.

 

[plugwash]

I have an old 800W microwave, is there a way that I could modify the transformer to power it.

Will that be the transformer with an output voltage measured in the thousands of volts which powers the magnetron? Now that we no longer have CRT TVs, the transformer in your microwave oven is the most lethal electrical component you can lay hands on in your home.

How do you think you might modify it to output a lower voltage?

You would have to completely replace the secondary. Some people do this to produce very low voltages at very high currents* but winding it for 24V would likely be a PITA

* https://www.youtube.com/watch?v=OZpBMfA9lZs

 

[Taylortwocities]

Here's one I prepared earlier

 

[ban-all-sheds]

https://www.youtube.com/watch?v=OZpBMfA9lZs

I'm glad I clicked that - initially I assumed it would be another Photonic Induction clip, but no.

Seen that madman before with his pulse-jet bicycle. Lord knows how he is still alive. Just one "lucky gene" away from being a Darwin Award winner.

 

[Robin0577]

I agree that rewinding transformers is not a job for a complete novice but it is perfectly possible to do it safely at home using fairly basic tools and equipment.

Until quite recently, Maplin used to sell DIY transformers with just a mains primary winding, ready for a custom secondary. I have some of these which I wound when I was a teenager that are still working well over 20 years later.

A microwave oven transformer, likely rated at 600-1000VA would probably make quite a good organ donor for a low voltage high current rewind.

I shall, however, refrain from giving instructions as I have no way of knowing if the OP has the skills to do it safely.

 

[JohnW2]

I agree that rewinding transformers is not a job for a complete novice but it is perfectly possible to do it safely at home using fairly basic tools and equipment.

Agreed (although how practical/possible {or not} it is is obviously depends upon the nature and design/construction of the tranny in question) - I've done it a good few times over the years, but ...

I shall, however, refrain from giving instructions as I have no way of knowing if the OP has the skills to do it safely.

... I would say that the OP's question ("what would I need to do?") has given us reasonable insight into the answer to that. I'm not getting at the OP, but if he needs to ask that question, I don't think he should be doing it.

Kind Regards, John

 

[stillp]

Ideally it needs to be 24V 40A at minimum, but it will work with lower inputs.

Could you explain that a little more please?

 

[333rocky333]

can some one enlighten ime what tran is in a microwave and why please.
also is there a risk in going in the thing to actually get it out

 

[JohnW2]

can some one enlighten ime what tran is in a microwave and why please.

There has to be a high voltage powerr supply for the magnetron - either a conventional one with a (real!) transformer or some sort of SMPSU - we don't even know whether the OP knows for sure that his has a conventional transformer.

...also is there a risk in going in the thing to actually get it out

a risk of what?

Kind Regards, John

 

[ban-all-sheds]

can some one enlighten ime what tran is in a microwave and why please.

One which puts out a few kV.

It is there because the magnetron which generates the microwaves needs kV to work.

http://s3.amazonaws.com/szmanuals/8b1cbf510190d2b758c9b5cb5e139167

also is there a risk in going in the thing to actually get it out

No risk getting it out, as long as the appliance is disconnected, and you discharge any power supply caps.

Quite a few risks in subsequent ignorant fiddling with it.

 

[333rocky333]

Thanks ban, I assume that example refering to 120 volt is because its american but I quess the principals the same.

never realised that, thought the only risk opening them was the radiation, obviously more danger than i expected

 

[flameport]

The main risk is that the transformer outputs a high voltage but also at a reasonably high current - easily enough to kill.

Most other easily available high voltage sources such as CRTs have very limited current capability.

There are also the capacitors which store sufficient energy to kill, the microwave radiation, the cancer causing toxic materials used in the magnetron etc.

 

[JohnW2]

Thanks ban, I assume that example refering to 120 volt is because its american but I quess the principals the same.

Indeed. AFAIAA, most traditional microwave ovens were like that - a transformer providing about 2kV followed by a simple diode/capacitor voltage doubler. That reduces the insulation requirements of the transformer, and the losses of a double-size secondary winding, as compared with having a 4kV tranny. As I mentioned, some of the more recent ones have some sort of SMPSU, rather than a 50Hz transformer.

never realised that, thought the only risk opening them was the radiation, obviously more danger than i expected

It's only electromagnetic radiation, so no risk from that when the power is off, and it's perfectly safe inside (when disconnected from power!) once the HV capacitor is discharged.

Kind Regards, John